PQgetf(3) libpqtypes Manual PQgetf(3)NAME
PQgetf - Gets one or more values from a PGresult in a scanf fashion.
SYNOPSIS
#include <libpqtypes.h>
int PQgetf(const PGresult *res, int tup_num,
const char *format, ...);
int PQgetvf(const PGresult *res, int tup_num,
const char *format, va_list ap);
DESCRIPTION
The PQgetf() and PQgetvf() functions get one or more field values from
a PGresult using a scanf style interface. The tup_num argument indi‐
cates which tuple to read values from; values can only be read from one
tuple at a time.
The format argument is a data type specifier string indicating the val‐
ues to retrieve, like %int4 or #timestamp. Any number of fields, in
any order, can be retrieved in a single call. Each data type specifier
has a cooresponding field_num, type-args, [...] contained within the
function´s variable argument list. The field_num either indicates
tuple field number or tuple field name, depending on whether the data
type in format used a ´%´ or ´#´ specifer mark (`man pqt-specs(3)´).
The type-args can be one or more arguments required by the specific
data type: for example, "%int4" would require a pointer to a PGint4.
All built-in PostgreSQL data types require a single pointer value.
RETURN VALUE
On success, a non-zero value is returned. On error, zero is returned
and PQgeterror(3) will contain an error message.
If the retrieval of any field fails, the get operation is aborted and
function will fail. Eventhough some fields may have succeeded prior to
the failure, their values should not be trusted. Instead, make another
PQgetf() call. Getting an array or a composite can lead to memory
leaks when getf fails. This is because these types allocate a PGresult
object that must be cleared. To avoid leaks, it is recommended to per‐
form cleanup even if getf fails, retrieve arrays and composites by
themselves or make them the last field in a getf call.
EXAMPLES
Using PQgetf on a PGresult
The example uses the libpq PQexec function to execute a query and then
uses PQgetf() to retrieve field values. It is important to note that
libpqtypes execution functions, like PQparamExec(3), do not need to
generate the PGresult provided to PQgetf().
int success;
PGint4 i4;
PGtext text;
PGbytea bytea;
PGpoint pt;
PGresult *res = PQexec(conn, "SELECT i,t,b,p FROM tbl");
/* Get some field values from the result (order doesn´t matter) */
success = PQgetf(res,
0, /* get field values from tuple 0 */
"%int4 #text %bytea %point",
/* type format specifiers (get text by name ´#´) */
0, &i4, /* get an int4 from field num 0 */
"t", &text, /* get a text from field name "t" */
2, &bytea, /* get a bytea from field num 2 */
3, &pt); /* get a point from field num 3 */
/* Output an error message using PQgeterror(3). */
if(!success)
fprintf(stderr, "*ERROR: %s\n", PQgeterror());
/* Output the values, do this before PQclear() */
else
printf("int4=%d, text=%s, bytea=%d bytes, point=(%f,%f)\n",
i4, text, bytea.len, pt.x, pt.y);
PQclear(res);
AUTHOR
A contribution of eSilo, LLC. for the PostgreSQL Database Management
System. Written by Andrew Chernow and Merlin Moncure.
REPORTING BUGS
Report bugs to <libpqtypes@esilo.com>.
COPYRIGHT
Copyright (c) 2011 eSilo, LLC. All rights reserved.
This is free software; see the source for copying conditions. There is
NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.
SEE ALSOpqt-specs(3), PQgeterror(3)libpqtypes 2011 PQgetf(3)
